The invention relates to automated manufacturing. It particularly relates to the monitoring of automated machine tools in process lines, manufacturing sites and other industrial settings, and will be described with particular reference thereto. However, the invention also finds application in other automated manufacturing processes where prompt scheduled maintenance or replacement of components of the manufacturing equipment is advantageous.
Typical materials processing lines or manufacturing sites include a plurality of machines, each performing one or more processing steps. The machines can, for example, be single- or multiple-spindle automatic screw machines, dial index/rotary transfer machines, transfer lines, or the like. Each machine in the process line typically includes a plurality of specialized tools that cut, drill, turn, polish, or otherwise work, process, or modify a work piece. Each machine usually operates on a cyclic basis systematically repeating a set of machine cycles that typically produce a single part per machine cycle. It is to be appreciated that some machines can produce more than one part per cycle.
In an industrial environment, an important consideration is maximizing throughput of such machinery. Hence, the machines preferably operate essentially continuously, each at a steady cyclic machine operating rate that produces the parts at a substantially constant rate.
However, materials processing machines typically involve cutting and/or abrasive interaction between the component tools or tool inserts and the work piece. This cutting and/or abrasion eventually results in a dulling of the tool cutting surfaces or other tool degradation which is usually correctable by sharpening the affected tool. Machines with dull tooling are periodically paused or taken off line to replace the dull tool with a freshly sharpened new tool or to perform other maintenance.
In an industrial environment, tool maintenance shutdowns are preferably anticipated and scheduled. An unanticipated shutdown, such as due to a catastrophic tool failure, can shut down operations at an inopportune time, e.g. when a delivery deadline is approaching. Scheduled replacement of tools is typically less expensive than recovering from a catastrophic failure of a degraded tool which may in turn affect or damage other tools or machines in the process line. Furthermore, replacement of tools on a schedule determined by the tool manufacturer's recommendation and/or past experience of the manufacturing site greatly reduces the likelihood of producing defective parts due to sub-standard or non-optimized machine tool performance. Scheduling tool replacements also assists in inventory maintenance because acquisition of the replacement tools can be appropriately scheduled. Lastly, overused and/or broken tooling usually cannot be simply resharpened and must be replaced at a typically large expense. A tool changed at the appropriate time can most often be resharpened and reused, thus extending its useful life.
Although the benefits of scheduled tool replacements are well recognized in industry, a problem arises in projecting the timing of such replacements and, thereafter, actually exercising the replacement. Typically, a component tool is assigned a tool life in terms of the number of machine cycles, e.g. a drill bit may be expected to perform adequately for 2,000 machine cycles. The number of tool life cycles will usually depend on several factors, including the type of workpiece, the material being machined, and the machine operating rate. For a typical process line, the cyclic tool life can be established by prior experience, e.g. by visually examining the tool after its removal to determine the extent of degradation. However, knowledge of tool life in terms of the number of cycles does not directly translate into a real-time projection of the actual tool life, e.g. in units of minutes, and more particularly into a realistic projection of the optimal time for replacing the tool.
The projection problem is exasperated by the environment of a typical industrial machine shops in which machine operators are attempting to cooperate with other machines and parts in the process line and are frequently working against short delivery schedules. This environment is not conducive to rigorously estimating and following tool replacement schedules. As a result, tools are often replaced at non-optimal times, resulting in unnecessary shutdowns, catastrophic tool failures, production of defective parts, higher tool costs, increased scrap material, inaccurate manufacturing cost estimation, and hosts of other negative consequences.
The prior art includes a number of systems directed toward monitoring machines to facilitate tool replacement or other maintenance. Many of these systems measure characteristics of the tool, such as vibration or power consumption, to detect and report impending or existing failure. These systems do not respond until after some detectable degradation of the tool has occurred, and do not project the timing of the replacement. These systems, therefore, are not proactive but, rather, are simply reactive.
U.S. Pat. No. 5,880,965 issued to Nakamura et al. discloses a method for analyzing work schedules to identify foreseeable problems. The method does not, however, monitor the actual performance of the manufacturing machines. U.S. Pat. No. 5,446,572 issued to Boldys discloses a system for tracking the number of machine cycles in which a tool is used, and also provides a visual indication of when the cycle count reaches warning and limit values. However, these values are reported in terms of machine cycles, so that the actual tool replacement time must be calculated as an additional step by machine operators who frequently are occupied in other tasks.
The present invention contemplates an improved tool wear monitoring system and method that overcomes the above-mentioned limitations and others.